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Friday, November 25, 2016

Flexible Hubs and Behavioral Mode

This sort of thing is on my mind at the moment, so I thought I'd bump it to the top of the queue, just to cement it in my mind (temporarily). Plus I've added abstracts from and links to the original research.

Now, research from Washington University in St. Louis offers new and compelling evidence that a well-connected core brain network based in the lateral prefrontal cortex and the posterior parietal cortex – parts of the brain most changed evolutionarily since our common ancestor with chimpanzees – contains "flexible hubs" that coordinate the brain's responses to novel cognitive challenges.

Acting as a central switching station for cognitive processing, this fronto-parietal brain network funnels incoming task instructions to those brain regions most adept at handling the cognitive task at hand, coordinating the transfer of information among processing brain regions to facilitate the rapid learning of new skills, the study finds.

"Flexible hubs are brain regions that coordinate activity throughout the brain to implement tasks – like a large Internet traffic router," suggests Michael Cole, PhD., a postdoctoral research associate in psychology at Washington University and lead author of the study published July 29 in the journal Nature Neuroscience.

This is in contrast to concepts of rigid modularity, where the brain is said to consist of quasi-autonomous behavioral modules, each dedicated to a specific perceptual, cognitive, or behavioral activity. These modules are conceived as being wired-in and universal across humans in a manner similar to, say, the skeletal system or the muscles. Barring pathology and injury, everyone's got the same set in the same arrangement. The notion of modes, and of behavioral hubs, allows for an open-ended arrangement of task specific configurations. The patterns of configuration are not wired-in, though many of the configured components would be.

Note: McCulloch was specifically interested in the reticular activating system, which is in the core of the brain and brain stem and is phylogenetically old. The structures pinpointed by Dr. Cole are in the cerebral cortex, which is a much newer structure. Beyond citing McCulloch's model Hays and I had no specific suggestions about other neural mechanisms that might be involved in modal organizing, though we talked informally about the need for such mechanisms.

Extensive evidence suggests the human ability to adaptively implement a wide variety of tasks is preferentially due to the operation of a fronto-parietal brain network. We hypothesized that this network’s adaptability is made possible by ‘flexible hubs’ – brain regions that rapidly update their pattern of global functional connectivity according to task demands. We utilized recent advances in characterizing brain network organization and dynamics to identify mechanisms consistent with the flexible hub theory. We found that the fronto-parietal network’s brain-wide functional connectivity pattern shifted more than other networks’ across a variety of task states, and that these connectivity patterns could be used to identify the current task. Further, these patterns were consistent across practiced and novel tasks, suggesting reuse of flexible hub connectivity patterns facilitates adaptive (novel) task performance. Together, these findings support a central role for fronto-parietal flexible hubs in cognitive control and adaptive implementation of task demands generally.

Control of thought and behavior is fundamental to human intelligence. Evidence suggests a frontoparietal brain network implements such cognitive control across diverse contexts. We identify a mechanism — global connectivity — by which components of this network might coordinate control of other networks. A lateral prefrontal cortex (LPFC) region’s activity was found to predict performance in a high control demand working memory task and also to exhibit high global connectivity. Critically, global connectivity in this LPFC region, involving connections both within and outside the frontoparietal network, showed a highly selective relationship with individual differences in fluid intelligence. These findings suggest LPFC is a global hub with a brainwide influence that facilitates the ability to implement control processes central to human intelligence.

Consensus across hundreds of published studies indicates that the same regions are involved in many forms of cognitive control. Using functional magnetic resonance imaging (fMRI), we found that these coactive regions form a functionally connected cognitive control network (CCN). Network status was identified by convergent methods, including: high interregional correlations during rest and task performance, consistently higher correlations within the CCN than the rest of cortex, co-activation in a visual search task, and mutual sensitivity to decision difficulty. Regions within the CCN include anterior cingulate cortex / pre-supplementary motor area (ACC/pSMA), dorsolateral prefrontal cortex (DLPFC), inferior frontal junction (IFJ), anterior insular cortex (AIC), dorsal pre-motor cortex (dPMC), and posterior parietal cortex (PPC). We used a novel visual line search task which included periods when the probe stimuli were occluded but subjects had to maintain and update working memory in preparation for the sudden appearance of a probe stimulus. The six CCN regions operated as a tightly coupled network during the ‘non-occluded’ portions of this task, with all regions responding to probe events. In contrast, the network was differentiated during occluded search. DLPFC, not ACC/pSMA, was involved in target memory maintenance when probes were absent, while both regions became active in preparation for difficult probes at the end of each occluded period. This approach illustrates one way in which a neuronal network can be identified, its high functional connectivity established, and its components dissociated in order to better understand the interactive and specialized internal mechanisms of that network.